Bark-beetle pests enduring cold, experts say

It may be freezing your water pipes and betraying the age of your car battery. But Colorado’s current cold snap still probably isn’t severe enough to significantly check the spread of bark beetles in the state’s forests.

Experts say that while the frigid weather may have some isolated effects on beetle populations, more widespread die-offs aren’t likely.

“There probably will be some local impacts, but as far as cleaning up all the mess at once, we’re probably not going to be that lucky,” said Tom Eager, a U.S. Forest Service entomologist based in Gunnison.

Bark beetles have spread across millions of acres of forests in the state, killing wide swaths of mountain pines. Sky Stephens, an entomologist with the Colorado State Forest Service, said the mountain pine beetle evolved to the conditions pine forests endure in the winter, even creating its own antifreeze to make it more resilient.

She said 72 hours of temperatures 30 degrees below 0 Fahrenheit can kill developing mountain pine beetles. But the temperature must be that low continuously, not just at night.

“Typically I tell people if we’re experiencing that kind of cold, we’re probably worried about other things,” she said.

She said that kind of temperature must occur beneath the bark, and snowpack can insulate beetles at the bases of trees.

Eager also noted that due to inversions, some of the worst of the recent cold temperatures have been in mountain valleys rather than the high country.

Stephens said there have been historical instances of deep freezes significantly impacting beetle numbers, but typically they have involved isolated areas. A freeze that kills some beetles in an area of low infestation could have a big impact on the population, but would hardly matter in areas of heavy infestation, she said.

Stephens said while there’s no controlling the weather, forests can be managed to reduce the chances of more such beetle epidemics. Past actions such as wildfire suppression reduced forest diversity, resulting in many trees of an age at which they have been highly susceptible to infestation in the current drought.

The mountain pine beetle infestation has had less impact in southwestern Colorado, which is toward the edge of the mountain pine’s range. But Eager said an ongoing spruce beetle infestation there has the potential to do similar amounts of damage, if not more.